The overall objectives represent an initial approach to understanding how a complex behavior develops under the influence of genetic and environmental factors into a flexible adaptation. The present research focuses on nest-building, especially as an expression of maternal behavior. We are utilizing both genetic and environmental manipulations in order to understand the contributions of each to individual differences in maternal behavior, as well as how both factors interact to result in true adaptation, i.e., the degree to which the ability to alter behavior in response to environmental change is under genetic control. Pilot studies on environmental influences emphasized the effects of temperature, and we are now concentrating on the role of hormones, especially as they mediate temperature effects.